A catalyst converter holding a catalyst is installed in an emission gas path of an internal combustion engine for the purpose of purifying the emission gas. A support holding a catalyst is used likewise also in a methanol reforming apparatus to generate hydrogen-rich gas by steam reforming of hydrocarbon compounds such as methanol, a CO removal apparatus to reform CO into CO2 to remove it, and a hydrogen combustion apparatus to burn H2 into H2O to remove it. A catalyst support is composed of many cells through which gas passes, and the wall surface of each of the cells is coated with a catalytic materials so as to have the-gas passing through the cells contact with the catalytic materials in a large contact area.
Either a ceramic catalyst support or a metal catalyst support is used as a catalyst support for the above purposes. The metal catalyst support is manufactured by winding a flat foil and a corrugated foil of a heat resistant alloy of several tens micrometers in thickness in layers, one over the other, to form a cylindrical metal honeycomb body, and encasing the metal honeycomb body in a cylindrical metal jacket. The honeycomb body is turned into a catalyst support by forming a catalyst holding layer impregnated with a catalytic materials on the wall surfaces of the honeycomb body cells through which the gas passes. The contact lines of the flat and corrugated foils of the honeycomb body formed through winding the foils are bonded by brazing or a similar bonding method of making the honeycomb body a strong structure.
A catalyst support used for purifying automobile emission gas is subjected to a violent thermal load during acceleration or high speed cruising of a vehicle as a result of high temperature emission gas passing through it. On the other hand, when an engine is idling or it is stopped, emission gas of a comparatively low temperature passes through it. Thus, heat cycles from high temperatures to low temperatures are repeated on the catalyst support and, therefore, a high structural reliability to withstand severe thermal stress and fatigue is required as the honeycomb body composing the catalyst support.
When a catalyst support is subjected to heating and cooling, a large temperature difference takes place between the center portion and the peripheral portion of the honeycomb body constituting the support: when the center portion is heated to a temperature higher than that of the peripheral portion, the center portion expands and, as a result, the peripheral portion undergoes a compressive stress; and when the center portion is cooled to a temperature lower than that of the peripheral portion, on the other hand, the center portion contracts and the peripheral portion is subjected to a tensile stress. Thus a large thermal stress is imposed on the peripheral portion in either case.
As shown in FIG. 2(a), Japanese Patent No. 2732889 and Japanese Examined Patent Publication No. H5-45298 disclose, inventions to bond a flat foil 3 and a corrugated foil 4 along their contact lines at a bonding portion 16 over the full axial length of the honeycomb body outer layers 12 for the purpose of preventing the fracture of the honeycomb body against the large thermal stress generated near its periphery, and to bond the foils only at a part of the axial length of the honeycomb body inner layers 13 (the layers other than the outer layers 12), more specifically only at a bending portion 17 which is located at the gas inlet end of the honeycomb body, for the purpose of minimizing the generated thermal stress as much as possible. Japanese Patent No. 2512622 discloses, as shown in FIG. 2(b), a honeycomb body in which the flat and corrugated foils are bonded only at a part of the prescribed axial length of the honeycomb body (a bonding portion 18 inside the honeycomb body over a cross section) and the foils are bonded also in the axial direction at the portion of the outermost 5 layers or less (a bonding portion 16 over the full axial length of the honeycomb body outer layers) for the same purpose.
When an automobile engine misfires, unburned gas combusts at the midst of honeycomb body and the temperature of the foils inside the honeycomb body exceeds their melting point. In the case of the above inventions wherein the foils are bonded only at the gas inlet end of the honeycomb body excluding the outer layers of the honeycomb body as shown in FIG. 2(a), if the foils melt inside the honeycomb body as a result of the misfire, the foils may protrude from the honeycomb body. Japanese Registered Utility Model No. 2543636 discloses, as shown in FIG. 2(c), a metal catalyst support free from the problem of protrusion of the honeycomb body or the like, wherein the flat and corrugated foils are bonded not only at the bonding portion 17 which is located at the gas inlet end of the honeycomb body but also at another bonding portion 18 inside the honeycomb body over a cross section which is located away from both ends thereof in the axial direction, as well as at the bonding portion 16 over the full axial length of the honeycomb body outer layers for the purpose of supporting the foils by the bonding portion 18 over the cross section even when the foils melt inside the honeycomb body as a result of a misfire.
In the above inventions wherein the flat foil 3 and the corrugated foil 4 constituting the honeycomb body are brazed only at a part or parts along their contact lines, a brazing filler metal is deposited only at the portions to be brazed and then the honeycomb body is heated to a high temperature to have the filler metal melt to braze those deposited parts of the contact lines of the flat and corrugated foils.
As a method of depositing the brazing filler metal only to the selected portions of the flat and corrugated foils, Japanese Unexamined International Patent Application No. H3-501363 discloses a method of applying an adhesive or a binding material to the areas to be brazed of any one of the flat and corrugated foils before winding them, then wind them in layers and feed the brazing filler metal in powder into the wound support, for the purpose of depositing it at the areas where the adhesive has been applied.
As a method of applying an adhesive to the areas to be later brazed of a flat or corrugated foil, Japanese Unexamined Patent Publication No. S56-4373 discloses a method of supplying an adhesive from an adhesive storage tank to the surface of a roll and applying the adhesive to the surface of a flat or corrugated foil by way of the roll.
At the contact lines of the flat and corrugated foils in a honeycomb body, the foils contact each other forming very acute angles, and the ends of the contact lines are exposed at both end faces of the honeycomb body. When a liquid, having good wettability with a metal foil and low viscosity, comes in contact with a honeycomb body at one or both end faces, it is sucked up along the contact lines of the flat and corrugated foils by the capillary phenomenon. Japanese Patent No. 2548796 discloses a method of brazing a honeycomb body characterized by sucking up a liquid adhesive along the contact lines of the flat and corrugated foils taking advantage of the capillary phenomenon by making the honeycomb body contact the surface of the liquid adhesive at one or both of the axial end faces, and then supplying a brazing filler metal in powder to have it deposited at the portions of the contact lines along which the adhesive has been sucked up. By this method, the adhesive is sucked up only along the contact lines of the flat and corrugated foils, it is not deposited at any other areas and, for this reason, the consumption of the brazing filler metal is controlled to the least and the problems such as corrosion by the brazing filler metal are avoided.
U.S. Pat. No. 5,082,167 discloses a method of sucking up an adhesive along the contact lines over the full axial length of the honeycomb body at outer layers by placing the honeycomb body on an annular base material holding the adhesive and, after that, of sucking up the adhesive to only one or both end portions of the honeycomb body by placing it on a cylindrical base material holding the adhesive and having an outer diameter equal to the inner diameter of the annular base material. According to this method, it is possible to braze the foils over the full axial length of the honeycomb body at outer layers and only at one or both end portions of the honeycomb body at inner layers by selecting the method of sucking up the adhesive.
A honeycomb body having a high structural reliability to withstand the thermal load and stress imposed on the catalyst support and being not broken in the event of an engine misfire can be manufactured by bonding the flat and corrugated foils over the full axial length of the honeycomb body at outer layers and also at an end of the honeycomb body at inner layers and/or a portion over a cross section of the honeycomb body at inner layers.
Another method of applying an adhesive to the wave tops of a corrugated foil before winding the flat and corrugated foils into a honeycomb body and then, after the winding, feed a brazing filler metal to the honeycomb body to have it deposited in the honeycomb body is also practiced. According to the method, the adhesive is applied to the wave tops of the corrugated foil by placing a pair of parallel rolls coated with the adhesive on their surfaces with a gap between them and making the corrugated foil pass through the gap and contact the roll surfaces only at the wave tops. By this method, however, if the gap between the parallel rolls is only a little too large, some of the wave tops of the corrugated foil may fail to come in contact with the surface of either of the rolls, causing the failure of the brazing and the consequent deterioration of structural strength and reliability as a result of no brazing at such portions. If the gap is only a little too narrow, on the other hand, the adhesive is applied to the wave tops of the corrugated foil over excessively large areas and the brazing filler metal in powder is deposited at all the areas covered with the adhesive. For this reason, the consumption of the filler metal becomes large and the metal foils constituting the honeycomb body are alloyed over a large area with the metal contained in the brazing filler material. This is undesirable since the alloying deteriorates mechanical properties of the foil.
A corrugated foil used for a honeycomb body is manufactured by applying plastic corrugation work to a flat foil. As a result of the plastic work, the surface of the corrugated foil may bend: for example, the wave tops may bend in the direction of foil width. In case of employing the above-mentioned method of applying the adhesive to the wave tops of a corrugated foil at the bonding portion over the full axial length of the honeycomb body outer layers using a pair of parallel rolls, if the adhesive is applied to such bent corrugated foil, the adhesive application on the concave side of the bending of the corrugated foil will be insufficient in the width center portion of the foil and too much at both the edges of the foil. On the convex side of the bending of the corrugated foil, on the contrary, the adhesive application will be too much at the width center portion of the foil and too little at both the edges.
Since an adhesive has to be applied to the foil over the full axial length of the honeycomb body at outer layer, it is necessary to prepare adhesive applicator rolls for this purpose. Further, since the adhesive has to be applied to one or both ends of the honeycomb body at inner layer and/or to a portion over a cross section of the honeycomb body inner layers, it is necessary to prepare another adhesive applicator rolls for these purposes. As a consequence, as long as a method of applying the adhesive using the applicator rolls is employed, plural sets of the applicator rolls are required and this has been a reason why the equipment cost of honeycomb body manufacturing facilities are high.
By the method of sucking up the adhesive from one or both ends of a honeycomb body, however, it has been impossible to apply the adhesive selectively to a bonding portion over a cross section of the honeycomb body inner layers. Therefore, it has been impossible to employ the method of sucking up an adhesive for manufacturing a honeycomb body conforming to the countermeasure against an engine misfire.